The present invention relates generally to an improved alternative for purge gas bubble gages for the monitoring of hydrostatic pressure at a submerged reference elevation that is customarily close to the bottom or bed of a body of water, to approximately determine the water depth, and is particularly concerned with a hydrostatic pressure equalizer apparatus for use in such systems.
It will be understood that dual systems may be employed for the monitoring of bulk density of liquids in the same manner that a dual system is shown on the front page of my U.S. Pat. No. 5,005,408. It will also be understood that the described technology is not limited to water, but is applicable to all liquids, as in tank gauging.
Various instruments are known for monitoring submerged pressure, and thus liquid level, in lakes, reservoirs, rivers, tanks, and other bodies of water or other liquids. One category of such liquid level monitoring instrument is a hydrostatic or purge gas pressure monitoring system, as described in my prior U.S. Pat. Nos. 5,005,408 and 5,315,876. In such systems, a small diameter piezometer line runs from an instrument shelter above the water or liquid surface down to a reference position near the bottom of the body of water. A trace flow of pressurized gas is passed down the tube, escaping as bubbles at the lower end. The pressure of gas escaping at the bottom of the tube is a function of the pressure of the medium into which it is bubbled, and the bubble gas pressure can be monitored by a suitable pressure responsive instrument secured to the upper end of the bubbler tube, as described in my previous patents referred to above. These systems are typically referred to as "bubble gages" in view of the release of bubbles into the liquid from the tube.
There are a number of problems with so-called bubble gages, such as errors incurred as a result of capillary effects and bubble release transients. In flood conditions, the bubbler line may become buried in sediment. It is very difficult to get bubbles to rise through sediment, with the result that pressure monitoring is difficult and inaccurate, if not impossible, under such conditions. Random errors of bubbler systems resulting from water rising in the bubble line, which often occurs under flood or tidal conditions, from bubble outlets being buried in sediment, and from bubble transients, are not possible to quantify with precision.